Antireflective surface structures for active and passive optical fiber

ABSTRACT

A method for creating a random anti-reflective surface structure on an optical fiber including a holder configured to hold the optical fiber comprising a groove and a fiber connector, an adhesive material to hold the optical fiber in the holder and fill any gap between the optical fiber and the holder, a glass to cover the adhesive material and the optical fiber, and a reactive ion etch device. The reactive ion etch device comprises a plasma and is configured to expose an end face of the optical fiber to the plasma. The plasma is configured to etch a random anti-reflective surface structure on the end face of the optical fiber.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. applicationSer. No. 16/185,219 filed on Nov. 9, 2018, which was a divisionalapplication of U.S. application Ser. No. 15/166,301 filed on May 27,2016, which claimed priority to U.S. Provisional Patent Application No.62/166,802 filed on May 27, 2015, the entire contents of each are hereinincorporated by reference.

GOVERNMENT INTEREST

The embodiments described herein may be manufactured, used, and/orlicensed by or for the United States Government without the payment ofroyalties thereon.

BACKGROUND Technical Field

The embodiments herein relate to optical systems, and more particularlyto antireflective surfaces used in optical systems.

Description of the Related Art

In optical systems, Fresnel reflections from an optical surface have avariety of undesirable effects. These may include reduced transmittance,feedback into laser systems, stray reflections, and in the case ofmilitary applications, potential detection by enemy combatants. In bulkoptics, Fresnel reflections are traditionally reduced using thin filmdielectric stacks of materials with alternating high and low refractiveindices. As a result of thin film interference effects, these stacks maybe designed to behave as antireflective (AR) coatings for a range ofwavelengths. Such coatings, however, may have several problemsassociated with them. For example, they may exhibit laser induced damagethresholds (LIDTs) significantly lower than those of the bulk optics,and may be subject to environmental degradations and delamination underthermal cycling, and may perform well only for a limited opticalbandwidth and angular range. It is desirable to prevent these issuesfrom occurring in an optical system.

SUMMARY

In view of the foregoing, an embodiment herein provides a system forcreating an anti-reflective surface structure on an optical device, thesystem comprising a shim comprising a textured pattern, wherein the shimis configured to stamp the optical device with the textured pattern; aconnector configured to place the optical device in proximity to theshim and apply a force to the optical device against the shim; and alaser source configured to heat the optical device by generating andapplying a laser beam to the optical device when the optical device isplaced in proximity to the shim.

The shim may comprise a transparent material, and wherein the lasersource is placed on an opposite side of the shim than the opticaldevice. The system may further comprise a pair of lenses configured tofocus the laser beam on the optical device. The laser source may belocated on the same side of the shim as the optical device. The laserbeam may be applied to the optical device from an oblique angle. Theshim may comprise a release layer comprising a non-adhesive material.

The release layer may comprise a thickness less than approximately 20nm. The laser source may comprise a CO₂ laser source creating awavelength of approximately 10.6 The optical device may comprise anoptical fiber, and wherein the anti-reflective surface structure may becreated on a tip of the optical fiber. The optical fiber may compriseany of silicate glass, oxide glass, halide glass, and chalcogenideglass, wherein the oxide glass may comprise any of aluminate, phosphate,germanate, tellurite, bismuthate, and antimonate glasses, wherein thehalide glass may comprise any of halogen elements, including fluorine,chlorine, bromine, and iodine, and wherein the chalcogenide glass maycomprise any of chalcogen elements including sulfur, selenium, andtellurium.

The optical fiber may comprise a single crystal comprising any ofyttrium aluminum garnet (YAG), sapphire, magnesium aluminate spinel,gadolinium gallium garnet (GGG), and lithium niobate. The optical fibermay be doped with rare earth ions of elements comprising any of cerium(Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm),europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium(Ho), erbium (Er), thulium (Tm), and ytterbium (Yb). The optical fibermay be doped with transition metal ions of elements comprising any oftitanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe),cobalt (Co), and nickel (Ni).

An embodiment herein provides a system for creating a randomanti-reflective surface structure on an optical fiber, the systemcomprising a holder, configured to hold the fiber optic, wherein theholder comprises any of a groove and a fiber connector, and wherein thefiber connector comprises any of a SMA, FC, and ST type connector; anadhesive material configured to hold the optical fiber in the holder andfill a gap between the optical fiber and the holder, wherein theadhesive material comprises a temporary adhesive material configured tobe removed; glass configured to cover the adhesive material and theoptical fiber; and a reactive ion etch device comprising plasma andconfigured to expose an end face of the optical fiber to the plasma,wherein the plasma is configured to etch the random anti-reflectivesurface structure on the end face of the optical fiber.

The plasma may comprise any of fluoride (F⁻), chloride (Cl⁻), C⁺⁴, oxide(O-2), B⁺³, sulfite (S⁻²), and argon (Ar) ions. The plasma may comprisean inductively coupled plasma (ICP). A pressure of the plasma may bemaintained between approximately 15 and 100 mT, and wherein a gas flowof the plasma may be maintained between approximately 20 and 150 sccm.The etching may be carried out until a peak-to-valley surface roughnessof the random anti-reflective surface structure is between approximately150 nm and 2 The system may further comprise an etch mask on the tips ofthe plurality of fibers, wherein the etch mask may comprise a layer ofmetal comprising a thickness less than approximately 1,000 nm, andwherein the metal may comprise any of gold (Au), silver (Ag), titanium(Ti), aluminum (Al), and chromium (Cr).

An embodiment herein provides a method for creating a randomanti-reflective surface structure on a plurality of optical fibers, themethod comprising placing the plurality of optical fibers in a pluralityof groves; holding the plurality of optical fibers in place using anadhesive; placing glass on the plurality of optical fibers; coating tipsof the plurality of optical fibers with a layer of metal, wherein themetal comprises any of gold (Au), silver (Ag), titanium (Ti), aluminum(Al), and chromium (Cr); and exposing the tips of the plurality ofoptical fibers to a plasma, wherein the plasma comprises any of fluoride(F⁻), chloride (Cl⁻), C⁺⁴, oxide (O⁻²), B⁺³, sulfite (S⁻²), and argon(Ar) ions.

These and other aspects of the embodiments herein will be betterappreciated and understood when considered in conjunction with thefollowing description and the accompanying drawings. It should beunderstood, however, that the following descriptions, while indicatingpreferred embodiments and numerous specific details thereof, are givenby way of illustration and not of limitation. Many changes andmodifications may be made within the scope of the embodiments hereinwithout departing from the spirit thereof, and the embodiments hereininclude all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein will be better understood from the followingdetailed description with reference to the drawings, in which:

FIG. 1A is a scanning electron microscope (SEM) image of the end facesof fibers in a V-groove holder according to an embodiment herein;

FIG. 1B is a schematic diagram illustrating an optical fiber accordingto an embodiment herein;

FIG. 1C is a schematic diagram illustrating a fiber bundle according toan embodiment herein;

FIG. 1D is a schematic diagram illustrating a system for etching asurface of an optical fiber according to an embodiment herein;

FIG. 2 is a SEM image of an etched optical fiber end face surfaceshowing both the core and clad areas according to an embodiment herein;

FIG. 3A is a schematic diagram illustrating a first part of a processfor stamping antireflective surface structures (ARSSs) used on anoptical fiber according to an embodiment herein;

FIG. 3B is a schematic diagram illustrating a second part of a processfor stamping ARSS on an optical fiber according to an embodiment herein;

FIG. 3C is a schematic diagram illustrating a third part of a processfor stamping ARSS on an optical fiber according to an embodiment herein;

FIG. 3D is a schematic diagram illustrating a fourth part of a processfor stamping ARSS on an optical fiber according to an embodiment herein;

FIG. 4A is a schematic diagram illustrating an optical fiber with ARSSpatterning according to an embodiment herein;

FIG. 4B is a schematic diagram illustrating an optical fiber with ARSSpatterning according to another embodiment herein;

FIG. 4C is a schematic diagram illustrating an optical fiber with ARSSpatterning according to still another embodiment herein;

FIG. 4D is a schematic diagram illustrating an optical fiber with ARSSpatterning according to still another embodiment herein;

FIG. 5 is a flowchart illustrating a method according to an embodimentherein; and

FIG. 6 is a flowchart illustrating a method according to anotherembodiment herein.

DETAILED DESCRIPTION

The embodiments herein and the various features and advantageous detailsthereof are explained more fully with reference to the non-limitingembodiments that are illustrated in the accompanying drawings anddetailed in the following description. Descriptions of well-knowncomponents and processing techniques are omitted so as to notunnecessarily obscure the embodiments herein. The examples used hereinare intended merely to facilitate an understanding of ways in which theembodiments herein may be practiced and to further enable those of skillin the art to practice the embodiments herein. Accordingly, the examplesshould not be construed as limiting the scope of the embodiments herein.

An approach for reducing Fresnel reflections while reducing the problemsassociated with traditional AR coatings is direct nano-patterning ofARSS on the surface of an optical material. Processing of thesestructures does not involve a permanent coating on the optic but insteadrelies on nano-patterning of the surface of the optical material itself.Nano-patterning of the surface may result in antireflective performanceof ARSS comparable to that of the traditional AR coatings, while addingsignificant advantages such as higher laser damage thresholds, widespectral bandwidths, and large acceptance angles.

ARSS structures may include providing a gradual transition in refractiveindex from one medium (medium A) to another (medium B). As light passesfrom A to B, the effective index in a given plane that is parallel tothe interface between A and B increases from that of A to that of B, asmore of the area of a given plane is composed of medium B. ARSSstructures may include arrays of nanoscale structures in which theperiod of the pattern is designed to be on a sub-wavelength scale inorder to avoid undesired diffraction effects, while the height of theindividual features is on the order of one-half the wavelength, in orderto simulate a graded index variation between air and the opticalsubstrate. An ARSS may have an ordered, repeating pattern. This istypically the case when an ARSS is created photolithographically orstamped with a patterned shim. Alternately, a random ARSS (rARSS) may becreated via an etch process.

Fiber tips may also be coated with AR dielectric stacks, as is the casewith bulk optics. Similar to reflections from bulk optics, reflectionsfrom fiber end faces are problematic for a variety of applications dueto reduced transmittance and feedback into laser systems. These problemsare especially severe in the case of high power laser applications whereAR coatings suffer from low LIDT and are subject to adhesion problems.

ARSS on fiber tips could provide AR performance while increasing LIDTand environmental stability. In an example, ARSS may be implemented onfiber tips in chalcogenide glass. The low softening point of theseglasses (typically less than approximately 300° C.) allows them to beheated and stamped with a patterned shim. In contrast, other types ofoptical fiber have much higher softening points. For example, silicafiber has a softening point greater than approximately 1400° C., makingthe stamping process provided by conventional techniques difficult.

An embodiment herein provides a method for patterning rARSS in anoptical fiber. In some embodiments herein, the rARSS may be patterned ona fiber through an etch process. In some embodiments herein, a patternmay be stamped on a fiber using a shim and a stamping procedure.Referring now to the drawings, and more particularly to FIGS. 1A through6, where similar reference characters denote corresponding featuresconsistently throughout the figures, there are shown preferredembodiments.

FIG. 1A is a SEM image of the end faces of fibers in a V-groove holderin an assembly 100 according to an embodiment herein. In an embodiment,the tips of fibers 102 are held in a holder. The holder, for example,may be one or more V-grooves 106, as shown in FIG. 1. In an embodiment,V-grooves 106 are grooves with a V-shaped cross section. Alternatively,in embodiments herein, the holder may be a groove having a cross sectionof any other shape. In an embodiment, the holder may be a glasscapillary, which, in turn, is mounted, in a semicircular fixture. Thefiber may be held in place with a suitable epoxy or other adhesive 108,and a cover glass 104 that may slide is placed on top of the assembly100 to aid in holding the fibers 102 in place. In an embodiment, theadhesive or epoxy may be temporary or removable, to allow removal of thefibers after etching.

FIG. 1B, with reference to FIG. 1A, is a schematic diagram illustratinga fiber 102 a according to an embodiment herein. The tip 120 of thefiber 102 a may optionally be coated with a layer 122 of metal, whichmay be less than approximately 1,000 nm thick. In an embodiment, themetal may comprise any of gold (Au), silver (Ag), titanium (Ti),aluminum (Al), and chromium (Cr). In an embodiment, the assembly 100 isheated and then cooled in order to allow the metal to condense into finedroplets. The metal acts as an etch mask in order to help initiatesurface texturing during patterning.

In an embodiment, the fiber 102 a may be held by a connector 124. In anembodiment, the fiber 102 a may be held by the connector 124 as analternative to one of the V-grooves 106. The connector 124 may compriseany of the FC, FC-APC, SMA, ST, and other commercially available orcustom-designed optical fiber connectors.

FIG. 1C, with reference to FIGS. 1A and 1B, is a schematic diagramillustrating a fiber bundle 130. In an embodiment, fibers 132, in thefiber bundle 130, may be connected by a connector 134. In an exemplaryembodiment, the fibers 132 may comprise a range of approximately 2 to10,000 fibers in close proximity. In an embodiment, the fibers 132 maybe fused or partially fused together. In an embodiment, the fibers 132may be separate and held in place mechanically or with suitable epoxy.In an embodiment, the end face of the bundle may be polished, and readyto be patterned.

FIG. 1D, with reference to FIGS. 1A and 1B, is a schematic diagramillustrating a system 150 according to an embodiment herein. In anembodiment, the assembly 100, including the fibers 102, may be placed ina reactive ion etch (RIE) system 152 with the fiber tips in the V-groovein a position where it will be exposed to plasma 154. In an embodiment,the fiber 102 a may be placed in the RIE. In an embodiment, the fiberbundle 130 may be placed in the RIE. An etch process may then be carriedout in the presence of suitable gases which may include any of fluoride(F⁻), chloride (Cl⁻), C⁺⁴, oxide (O⁻²), B⁺³, sulfite (S⁻²), and argon(Ar) ions. In an embodiment, an inductively coupled plasma (ICP) isused. The pressure of the plasma 154 may be maintained betweenapproximately 15 and 100 mT, and the gas flow is maintained betweenapproximately 20 and 150 sccm. Etching may be carried out untilpeak-to-valley surface roughness is between approximately 150 nm and 2μm.

FIG. 2, with reference to FIG. 1A and FIG. 1B, shows an SEM image of asurface morphology of the fiber end face after etching, according to anexemplary embodiment herein. FIG. 2 reveals a similar appearance for acore 202 and clad areas 204 of the fiber 200 (although the two regionsare still distinguishable due to differences in the core and cladrefractive indices, the dashed circle on FIG. 2 is added solely forillustration purposes and to generally show the boundary of the core202).

In an exemplary embodiment, the fiber 200 comprises a single mode silicaoptical fiber (SMF28). In an exemplary embodiment herein, thefabrication of rARSS on the end faces of the single mode silica opticalfiber (SMF28) 102 is achieved using the system 150 of FIG. 1B. Forprocessing the fiber 200 in the RIE system 152, an end of the fiber 200is mounted with epoxy or adhesive 108 in a V-groove of the V-grooves 106of the assembly 100 as shown FIGS. 1A and 1B. The end of the fiber 200is etched as described with reference to FIGS. 1A and 1B.

In an exemplary embodiment herein, the measured transmission per endface on a fiber with rARSS is increased to approximately 99.3% atapproximately 780 nm wavelength, and approximately 99.4% atapproximately 1,550 nm wavelength. This compares favorably to anuntreated fiber, which has an end face transmittance of approximately96.5% at these wavelengths.

In an exemplary embodiment herein, laser damage testing was performed at1.06 μm on the end faces of the fiber 200 and untreated silica fibers.The laser parameters are a 20 nsec pulsewidth, a 20 Hz pulse repetitionrate, and spot size of 8.7 μm (at 1/e²) which nearly matches the fibercore diameter (8.2 μm). A total of 600 laser shots irradiated the fiberend faces at increasing fluence until damage occurred. The resultsobtained, as summarized in Table 1, show remarkably high laser damagethresholds, up to 850 J/cm² for silica fiber end faces with ARSS, whichapproaches that of the untreated fiber.

TABLE 1 Laser damage threshold values at 1.06 μm for fused silica SMF28optical fibers Fiber Array Threshold I.D. Fiber Type (J · cm⁻²) Type ofDamage #00 uncoated #1 650 end-face #00 uncoated #2 1000 end-face #13ARSS #1 700 end-face #13 ARSS #2 750 end-face #17 ARSS #3 750 end-face#17 ARSS #4 850 end-face

FIGS. 3A through 3D, with reference to FIGS. 1A through 2, are schematicdiagrams illustrating systems for creating an ARSS pattern according tosome embodiments herein. FIG. 3A illustrates an embodiment where the tipof a fiber 306 is placed in close proximity or contact with a patternedshim 302 with the fiber optionally held in a fiber connector 304. Thetextured shim 302 may be made from silicon or another metal or ceramicwith a melting temperature higher than that of silica. The textured shim302 may be coated with a release layer 308. The release layer 308 maycomprise a material that does not adhere strongly to either the fiber306 or the shim 302. In an exemplary embodiment, the release layercomprises any of boron nitrite and molybdenum disulfide. In anembodiment, the release layer 308 comprises a thickness less thanapproximately 20 nm. In an embodiment, a force may be applied to thefiber 306 against the shim 302 using the fiber connector 304 when placedin close proximity or contact with the patterned shim 302.

FIG. 3B, with reference to FIG. 3A, is a schematic diagram illustratinga system 330 for creating an ARSS pattern according to some embodimentsherein. In an embodiment, the tip of the fiber 306 may be heated with alaser beam 332. The fiber 306 may then be pressed against the shim 302so that the pattern of the shim 302 is imprinted on the tip of the fiber306.

The laser beam 332 is created by a laser source 334. In an embodiment,the laser source 302 comprises a CO₂ laser source that creates anemission at a wavelength of approximately 10.6 In another embodiment,other laser sources with a wavelength readily absorbed by the opticalfiber 306 may be used. If the shim 302 is completely or partiallytransparent to the laser radiation 332 (e.g., 10.6 μm radiation passingthrough a silicon shim), it may be focused on the fiber tip through theshim 302 using a pair of lenses 336.

FIG. 3C, with reference to FIGS. 3A and 3B, is a schematic diagramillustrating a system 360 for creating an ARSS pattern according to someembodiments herein. In the system 360, a laser source 362 is located onthe same side of the shim 302 as the fiber 306, and it produces a laserbeam 364 that may be focused on the tip of the fiber 306 from an obliqueangle. In an embodiment, the tip of the fiber 306 is heated for asufficiently long enough period of time that the glass softens andconforms to the surface structure of the shim 302, thereby transferringthe pattern from the shim 302 to the fiber 306. FIG. 3D, with referenceto FIGS. 3A through 3C, is a schematic diagram illustrating the fiber306 and the fiber connector 304 removed from the shim 302, resulting ina fiber face stamped with an ARSS pattern.

Embodiments provided herein may dramatically reduce surface reflectionsfrom a fiber end face. For example, using the embodiments herein, thereflection from a silica fiber end face is reduced from approximately3.5% to less than approximately 0.1%. Using embodiments herein, theanti-reflective property of the component remains optically broadband,with low reflection over a spectral range that is typically greater thanapproximately 500 nm.

The embodiments herein provide reduced surface reflection that serves toincrease fiber throughput and prevent back reflections that can bedetrimental to the performance of lasers and other optical components.The embodiments herein further result in a significantly higher LIDT incomparison to an AR-coated fiber.

In an embodiment herein, the fiber used, for example the fiber 102, 200,306 may comprise any of a silicate glass. In some embodiments, the fibermay comprise any of an oxide glass other than a silicate glass. Theoxide glass may comprise any of aluminate, phosphate, germanate,tellurite, bismuthate, and antimonate glasses. In an embodiment herein,the fiber may comprise a halide glass. Halide glasses comprise any ofhalogen elements, including fluorine, chlorine, bromine, and iodine, orcombinations thereof. In an embodiment herein, the fiber may comprise achalcogenide glass. Chalcogenide glasses comprise any of chalcogenelements including sulfur, selenium, and tellurium, or combinationsthereof.

In an embodiment herein, the fiber may comprise a single crystal ratherthan glass. The single crystal may be any optically transmissivecrystalline material that is readily drawn into a fiber form. Thecrystalline material may comprise any of yttrium aluminum garnet (YAG),sapphire, magnesium aluminate spinel, gadolinium gallium garnet (GGG),and lithium niobate. In an embodiment, the ARSS as described herein maybe fabricated on a fiber doped with rare earth ions of elementscomprising any of cerium (Ce), praseodymium (Pr), neodymium (Nd),promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium(Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), andytterbium (Yb). In an embodiment herein, the ARSS may be fabricated on afiber doped with transition metal ions of elements comprising titanium(Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt(Co), and nickel (Ni).

In embodiments herein, the fiber 102, 200, 306 used may comprise anactive or a passive optical fiber. In an embodiment, the fiber 102, 200,306 may be removed from its holder, for example V-grooves 106 in FIG. 1Aor fiber connector 304 in FIGS. 3A through 3D, after the ARSSpatterning. The fiber 102, 200, 306 may then be connected or mounted inanother holder.

FIG. 4A, with reference to FIGS. 1A through 3D, illustrates a fiber 400with ARSS according to an embodiment herein. The fiber 400 comprisesundoped sections 402 and 406, and a doped section 404. In an embodiment,the ARSS may be fabricated on the surface 408 of the undoped section402. In an embodiment, the section 402 may be spliced or bonded onto thedoped section 404.

FIG. 4B, with reference to FIGS. 1A through 4A, illustrates a fiber 420with ARSS according to an embodiment herein. In an embodiment herein,the ARSS 424 may be patterned on a thin glass endcap 426. The endcap 426may be attached to an untreated fiber 422 via fusion splicing or opticalcement.

FIG. 4C, with reference to FIGS. 1A through 4B, illustrates a fiber 430with ARSS according to an embodiment herein. In an embodiment, the fiber430 may be tapered to reduce its diameter, and an ARSS pattern 432 maybe applied to the side rather than the end face of the fiber 430. Thisstructure may couple light out of the fiber, serving to reducecladding-coupled light, reduce transmission in higher order modes, ordump unabsorbed pump light. FIG. 4D, with reference to FIGS. 1A through4C, illustrates a fiber 440 with ARSS according to an embodiment herein.In an embodiment, the fiber 440 may be tapered in the middle to reduceits diameter, and an ARSS pattern 442 may be applied to the taperedsurface of the fiber 440.

In an embodiment, a fiber tip that is composed of either a silicateglass or non-silicate material could be coated with a film of silica,with a thickness greater than approximately 500 nm, and this film maysubsequently be patterned according to any of the embodiments providedherein.

FIG. 5, with reference to FIGS. 1A through 1D, is a flowchartillustrating a method 500 for creating a rARSS pattern on optical fibers102, according to an embodiment herein. At step 502, optical fibers 102may be placed in one or more grooves 106. At step 504, the opticalfibers 102 and held with adhesive 108. At step 506, the cover glass 104may be placed on the optical fibers 102. At step 508, a tip 120 of theoptical fiber 102 a may be coated with the metal layer 122. The metalmay comprise any of gold (Au), silver (Ag), titanium (Ti), aluminum(Al), and chromium (Cr). At step 510, the tips of the optical fibers maybe exposed to plasma 154. The plasma may comprise any of fluoride (F⁻),chloride (Cl⁻), C⁺⁴, oxide (O⁻²), B⁺³, sulfite (S⁻²), and argon (Ar)ions.

FIG. 6, with reference to FIGS. 3A through 3D, is a flowchartillustrating a method 600 for creating an ARSS pattern on an opticalfiber. At step 602, the optical fiber 306 is held against the patternedshim 302. At step 604, the optical fiber 306 is heated using the laser334. The laser 334 may be a CO₂ laser. At step 606, the pattered shim308 is pressed against the optical fiber 306 to create the ARSS pattern.In an embodiment, methods 500 or 600 may be used to create the ARSSpattern using any of the assembly 100 in FIG. 1A and the fiber bundle130 in FIG. 1C.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the embodiments herein that others can, byapplying current knowledge, readily modify and/or adapt for variousapplications such specific embodiments without departing from thegeneric concept, and, therefore, such adaptations and modificationsshould and are intended to be comprehended within the meaning and rangeof equivalents of the disclosed embodiments. It is to be understood thatthe phraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, while the embodimentsherein have been described in terms of preferred embodiments, thoseskilled in the art will recognize that the embodiments herein can bepracticed with modification within the spirit and scope of the appendedclaims.

What is claimed is:
 1. A method for creating a random anti-reflectivesurface structure on a plurality of optical fibers, said methodcomprising: placing a plurality of optical fibers in a plurality ofgroves; holding said plurality of optical fibers in place using anadhesive; placing a glass on said plurality of optical fibers; coatingtips of said plurality of optical fibers with a layer of metal, whereinsaid metal comprises any of gold (Au), silver (Ag), titanium (Ti),aluminum (Al), and chromium (Cr); and exposing said tips of saidplurality of optical fibers to a plasma, wherein said plasma comprisesany of fluoride (F⁻), chloride (Cl⁻), C⁺⁴, oxide (O⁻²), B⁺³, sulfite(S⁻²), and argon (Ar) ions.
 2. The method of claim 1, wherein saidplasma comprises an inductively coupled plasma (ICP).
 3. The method ofclaim 1, wherein a pressure of said plasma is maintained betweenapproximately 15 and 100 mT, and wherein a gas flow of said plasma ismaintained between approximately 20 and 150 sccm.